This document relates to semiconductor integrated circuits (ICs), and more particularly to assemblies with semiconductor integrated circuits.
Multiple ICs can be combined in a high-density assembly to provide needed functionality. High density is desired for small assembly size and also to shorten electrical paths as needed for high speed and low power consumption. However, a small IC is a fragile device with tiny, densely packed contact pads which must be connected to possibly larger contact pads of other integrated or non-integrated (discrete) circuits. To enable such connections, an intermediate IC (interposer) can be provided. Interposers may also increase the mechanical strength of the assembly, absorb stresses generated due to differences in coefficients of thermal expansion (CTE), and improve the ability to dissipate heat that can be generated during operation or manufacture. However, interposers increase the assembly size and complexity, and they should be as thin as possible to shorten the electrical connections through the interposers.
FIG. 1 illustrates an exemplary assembly 102 with interposers as described in U.S. pre-grant patent publication 2007/0235850 by Gerber et al., published Oct. 11, 2007, incorporated herein by reference. The assembly is connected to external devices 104.2, 104.1 by large solder balls 108. The assembly includes ICs 110.1, 110.2 attached from the bottom to respective larger ICs (interposers) 120.1, 120.2. A typical IC is fabricated in a wafer, and an IC can occupy a whole wafer, but an IC can also be part (“chip” or “die”) of a wafer. In FIG. 1, ICs 110 (i.e. 110.1, 110.2) are dies attached to the interposers by connections 140 which are smaller, and denser packed, than solder connections 108. Interposers 120 are thicker and wider than dies 110.
In regions not occupied by die 110.2, interposer 120.2 is connected to interposer 120.1 by studs 154. In regions not occupied by die 110.1, interposer 120.1 is connected to an underlying insulator-based substrate 160 by other studs 154.
Each interposer 120 includes interconnects 158 each of which goes through the interposer and interconnects the interposer's circuits (not shown) coupled to connections 108, 140, 154. Insulator-based substrate 160 includes similar interconnects 164.
In manufacturing, ICs 110 and 120 and substrate 160 are separately manufactured and then attached to each other. Then the portion of assembly 102 above the substrate 160 is covered by an encapsulant (e.g. molding compound) 180 to mechanically strengthen the assembly. The assembly is then attached to external devices 104.
As noted above, it is desirable to reduce CTE mismatches, and thus the ICs 110 and 120 and the encapsulant 180 should preferably be made of materials with similar CTEs. However, a typical encapsulant (epoxy) has a much higher CTE than many ICs based on semiconductor materials such as silicon, so there is a need to reduce the encapsulant amount while still obtaining a robust assembly. Also, it is desirable to improve the mechanical strength and heat dissipation of intermediate structures obtained during manufacturing as well as the final structure.